The present invention relates to an apparatus and method for transforming between a discrete cosine transform (DCT) coefficient and a discrete wavelet transform (DWT) coefficient, and more particularly, to an apparatus and method for transforming between a 2-dimensional 8×8 DCT coefficient, which is used in the moving picture compression standard, and a 2-dimensional 1-level DWT coefficient, which is used in JPEG2000 (Joint Photographic Experts Group 2000) that is the wavelet-based image compression standard.
With the development of communication technology and multimedia technology, multimedia data are provided through wired/wireless communication networks such as internet, mobile communication networks and so on. Multimedia data are formed in various formats depending on their type and use, and are compressed in various compression standards in consideration of the transmission efficiency on the network. For example, MPEG2 (Moving Picture Experts Group 2) and MPEG4 use 2-dimensional 8×8 DCT, while JPEG2000 uses 2-dimensional DWT.
Domain transform such as DCT is widely used in the field of signal processing. The DCT is used in JPEG image compression, and MJPEG, MPEG, and DV video compression. Herein, the 2-dimensional DCT of N×N blocks are computed and the results are quantized and entropy-coded. In this case, N is typically 8 and the DCT formula is applied to each row and column of the block. The result is an 8×8 transform coefficient matrix in which a (0,0) element is a DC component and entries with increasing vertical and horizontal index values represent higher vertical and horizontal spatial frequencies.
Meanwhile, JPEG2000 has been recently proposed as the new compression standard for still images. The JPEG 2000 uses DWT and provides a much higher compression rate than the conventional DCT-based JPEG. Also, the JPEG2000 is superior in the quality of decompressed images.
As the new still image compression standard is proposed, there is a need in the art for transforming between DCT used in the conventional image compression standard and DWT used in the new image compression standard. In particular, there is a need in the art for transforming between a DWT coefficient and a DCT coefficient in order to transcode a DWT-compressed image of the new standard JPEG 2000 into a DCT-compressed image of the conventional standard JPEG, and vise versa. However, up to now, there is no method capable of transforming between a DCT coefficient and a DWT coefficient.